FIG. 1 shows a typical lighting system, including an electronic converter 10 and at least one lighting module 20. Generally speaking, a lighting module 20 includes one or more light radiation sources, including e.g. at least one LED (Light Emitting Diode) or other solid-state lighting means, such as laser diodes.
Specifically, in the presently considered example, the electronic converter is an AC/DC converter. Therefore, the electronic converter 10 includes two input terminals 102a and 102b, for the connection to the mains, and two output terminals 104a and 104b for the connection to the lighting module(s) 20. Typically, line 102a is connected to phase L and terminal 102b is connected to neutral N.
For example, FIG. 1 shows a lighting system wherein the electronic converter 10 is a voltage generator, and similarly the lighting module 20 is a module configured to be supplied with a voltage.
Therefore, in FIG. 1, the electronic converter 10 receives at input, via terminals 102a and 102b, an alternating voltage Vin, such as e.g. 110 or 230 VAC, and provides at output, via the positive terminal 104a and the negative terminal 104b, a regulated voltage Vout, such as e.g. 12 or 24 VDC.
For example, FIG. 2 shows an example of a lighting module 20 configured to be supplied by a regulated voltage Vout. Specifically, lighting module 20 include a positive input terminal 200a and a negative input terminal 200b, for the connection to the terminals 104a and 104b of the electronic converter 10. For example, lighting module 20 may be connected, directly or through a cable, to the electronic converter 10. Therefore, terminal 200a is connected to positive terminal 104a, and terminal 200b is connected to negative terminal 104b, and the lighting module thus receives the voltage Vout.
In the presently considered example, the lighting module 20 is a LED module including one or more LEDs L (or laser diodes), which are connected between the terminals 200a and 200b. For example, module 20 may include a chain or string of LEDs 22, wherein a plurality of LEDs L (or laser diodes) is connected in series. Moreover, the LEDs L (or laser diodes) may also be divided along various branches connected in parallel. For example, as shown in FIG. 2, module 20 may include a first string of LEDs 22a including a first group of LEDs L connected in series, and a second string of LEDs 22b including a second group of LEDs L connected in series. Similarly, a plurality of lighting modules 20 may be connected in parallel to the terminals 104a and 104b. 
Given that the lighting module 20 is supplied with a voltage, the lighting module 20 typically includes a current regulator 24, which is connected in series with each string of LEDs 22. For example, the first string of LEDs 22a and a first current regulator 24a are connected (e.g. directly) in series between the terminals 200a and 200b, and the second string of LEDs 22b and a second current regulator 24b are connected (e.g. directly) in series between the terminals 200a and 200b. Therefore, in the presently considered example, strings 22a and 22b (and similarly the string of LEDs of other lighting modules) are supplied with a common voltage (Vout).
In the simplest of cases, the current regulator 24 may be a resistor or a linear current regulator. The current regulator 24 may also be implemented with current mirrors or with a switched mode current regulator, typically including an inductor and an electronic switch.
As a safety measure, the electronic converter 10 is often required to be an insulated converter. Therefore, in such an instance, the electronic converter 10 includes at least one transformer T, including a primary winding T1 and a secondary winding T2.
For example, FIG. 3 shows the schematic operation diagram of a switched mode electronic converter 10.
In this case, converter 10 includes, between the input terminals 102a and 102b and the primary winding T1 of transformer T, a rectifier circuit 108 and a switching stage 112.
Specifically, the input of the rectifier circuit 108, such as e.g. a diode bridge, is connected (e.g. directly) to terminals 102a and 102b. Therefore, the rectifier circuit 108 receives at input the input voltage Vin and provides at output a DC voltage Vin,DC.
Generally speaking, between the input terminals 102a and 102b and the rectifier circuit 108 there may also be provided a filter circuit 106, configured to filter the noise produced by the electronic converter.
The switching stage 112 includes one or more electronic converters, which are adapted to selectively connect the terminals of the primary winding T1 of transformer T to voltage Vin,DC supplied by the rectifier circuit 108.
Generally speaking, between the rectifier circuit 108 and the switching stage 112 there may be provided a filter circuit 110, such as e.g. a capacitor connected in parallel with the output terminals of the rectifier circuit 108. Therefore, in the present case, the filter circuit 108 receives (e.g. directly) voltage Vin,DC and supplies at output a filtered voltage, typically known as bus voltage Vbus. In this case, therefore, the switching stage 112 receives at input voltage Vbus.
Said alternating voltage to the secondary side is subsequently converted by a rectifier circuit 114, typically including one or more diodes (such as e.g. a diode bridge), into a DC voltage. Therefore, the input of the rectifier circuit 114 is connected (e.g. directly) to the terminals of the secondary winding T2 of transformer T, and provides at output a DC voltage which, in the simplest of cases, corresponds to the output voltage Vout. Preferably, there is provided a filter circuit 116 connected between the output of the rectifier circuit 114 and the output of converter 10, i.e. the terminals 104a and 104b. Therefore, the filter circuit 116 is configured to stabilize the voltage provided by the rectifier circuit 114. For example, possible rectifier circuits 114 (optionally employing a transformer with an intermediate connection) and filter circuits 116 are described in document PCT/IB2016/055923, the content whereof is incorporated herein by way of reference.
Thus, in a switching converter, transformer T receives on the primary side an alternating voltage having a switching frequency determined by the switching stage 112. Typically, the switching frequency is in the range between 1 kHz and 200 kHz, preferably between 20 kHz and 200 kHz. One or more capacitors CY may often be connected between the primary winding T1 and the secondary winding T2, in order to filter a possible common mode noise.
The electronic converter 10 moreover includes a control circuit 118, configured to generate one or more driving signals DRV for driving the switching stage 112, so as to regulate the output voltage Vout to a desired value. Generally speaking, the control circuit 118 may be any analogue and/or digital circuit, such as e.g. a microprocessor programmed via software code.
To this end, a feedback circuit 120 is typically provided which supplies a feedback signal FB, which is determined as a function of the output voltage Vout. Typically, the feedback circuit 120 includes an optocoupler (in order to enable an insulated feedback) and optionally an error amplifier, typically a PI (Proportional-Integral) or PID (Proportional-Integral-Derivative) regulator.
This general architecture of a switched mode electronic converter is described e.g. in document US 2012/0275195 A1. The various topologies of switched mode electronic converters are well known; the main topologies (flyback, forward, etc.) are described e.g. in L. Wuidart, “Application Note—Topologies For Switched Mode Power Supplies”, STMicroelectronics, 1999.
As shown in FIG. 4, generally speaking, the electronic converter 10 may also be a DC/DC electronic converter.
In this case, the input terminals 102a and 102b are connected to a DC voltage generator, such as a battery, or the input voltage Vin is a DC voltage. In this case, the rectifier circuit 108 is not mandatory, and the optional filter circuits 106 and 110 may be combined into one filter circuit. As for the other features, the architecture corresponds to FIG. 3.
The light emitted by the light radiation sources of the lighting module 20 is often also required to be adjustable, offering therefore a so-called dimming function.
Specifically, as shown in FIG. 5, the electronic converter 10 shown in FIG. 3 or 4 may include at output a switching stage 122 including one or more electronic switches. Specifically, said switching stage 122 is configured to enable or disable the output of electronic converter 10.
For example, in FIG. 5, the switching stage 122 includes an electronic switch SW connected in series with the lighting module 20. For example, said electronic switch SW may be connected (e.g. directly) between the negative terminal of the filter circuit 116 and the negative output terminal 104b. Therefore, in the presently considered example, the switch SW is a low-side switch, and may be implemented with an re-channel FET (Field-Effect Transistor).
The control circuit 118 may therefore generate a driving signal CTRL (which is suitably transmitted to the secondary side of transformer T) for said switching stage 122, specifically the electronic switch SW, as a function of a dimming signal DIMM. According to this solution, converter 10 therefore performs the dimming operation by regulating the average current flowing through the lighting module 20, by switching on/off the output of converter 10 and therefore the lighting module 20. For example, for this purpose a Pulse Width Modulation (PWM) driving signal CTRL is often used, wherein the control circuit 118 varies the duty cycle of said signal CTRL as a function of the dimming signal DIMM. Typically, the frequency of the PWM modulation is in the range between 100 Hz and 2 kHz. Generally speaking, the dimming signal DIMM may be any analogue or digital signal. Generally speaking, the dimming signal DIMM may be received through a further terminal 102c of the electronic converter 10, and/or it may be generated internally, e.g. as a function of other signals, e.g. a signal indicative of the brightness of the light in the environment.
Generally speaking, the dimming function and specifically stage 122 may also be implemented in a separated device, i.e. a so-called dimmer.
As shown in FIG. 6, in this case the electronic converter provides (as described with reference to FIGS. 3 and 4) a voltage Vout. However, a device/dimmer 30 is interposed between the electronic converter 10 and the lighting module 20, therefore switching the supply to lighting module 20 on or off. Specifically, in this architecture, device 30 includes two terminals 302a and 302b, for the connection to the terminals 104a and 104b of the electronic converter 10. Moreover, the device 30 includes two terminals 304a and 304b for the connection to the terminals 200a and 200b of the lighting module 20 (or to the first lighting module in a chain of modules); in other words, the lighting module 20 is connected (e.g. via a cable) to the terminals 304a and 304, and not directly to the terminals 104a and 104b of the electronic converter 10.
Similarly to what has been described with reference to FIG. 5, device 30 includes a switching stage 122, including one or more switches adapted to interrupt the electrical connection between the terminals 302a and 304a and/or between the terminals 302b and 304b. For example, FIG. 6 shows an electronic switch SW which is connected between terminals 302b and 304b, i.e. the negative terminals. The device/dimmer 30 moreover includes a control circuit 306 which generates a control signal CTRL, such as e.g. a PWM signal, for driving switch SW (also see the description of FIG. 5). Typically, the device/dimmer 30 also includes a sensor 308, which supplies a dimming signal DIMM indicative of the required brightness, or the control circuit 306 generates the driving signal CTRL as a function of the dimming signal DIMM. For example, sensor 308 may be a light sensor, a user interface, e.g. a potentiometer, for directly varying the dimming signal DIMM, and/or an infrared or radiofrequency detector for receiving a signal transmitted by a remote control.
The electronic converters 10 described with reference to FIGS. 3 to 6 offer the advantage that, by using a transformer T having a suitable electrical insulation (e.g. a double or reinforced insulation) between the primary winding T1 and the secondary winding T2, the output voltage Vout may be a SELV (Safety Extra-Low Voltage). To this end, the components which are supplied with high voltage, i.e. the components on the primary side of transformer T (blocks 106 to 112) are typically mounted within a housing of an insulating material.
For example, FIGS. 7a and 7b show two views (from above and from the side) of an electronic converter 10.
In the presently considered example, the components of electronic converter 10 are mounted on a printed circuit 124. For example, the terminals 104a and 104b of the electronic converter 10 may be implemented via quick connection means, such as e.g. a screw or spring terminal block having e.g. two contacts. Similarly, the terminals 102a and 102b for the connection to the mains/battery and optionally the terminal 102c for the dimming signal DIMM may be implemented via quick connection means, e.g. terminal blocks.
In order to protect the user from electrocution, the other components (at least the components on the primary side, and preferably all the blocks 106-122 and transformer T) of the electronic converter 10 are mounted within a housing 126, typically of an insulating material such as a plastic material. In the presently considered example, the converter 10 is therefore a class II device, having no ground connection, but the high voltage components are protected by an electrical insulation. Generally speaking, the term class II does not necessarily imply that the housing is insulating, but that a double insulation is present between the outer surfaces thereof and the mains.
FIGS. 8a and 8b show two views (from above and from the side) of a lighting module 20.
Specifically, also the components of the lighting module 20 may be mounted onto a printed circuit 202, optionally a flexible printed circuit. Moreover, also the terminals 200a and 200b of the lighting module 20 may be implemented by quick connection means, such as e.g. a screw or spring terminal block having e.g. two contacts. Additionally, the lighting module 20 often includes two further terminals 200′a and 200′b, which are internally connected to terminals 200a and 200b, i.e. such terminals supply voltage Vout as well. Therefore, said terminals may be used for connecting the terminals 200a and 200b of a further lighting module to the terminals 200′a and 200′b of the lighting module 20, and not directly to the terminals 104a and 104b of the electronic converter 10.
Also the components of the lighting module 20 are often protected, e.g. by a housing 204 and/or protection layers, e.g. silicone layers. However, as voltage Vout is low, said protection is mainly destined to protect the components from a mechanical point of view (e.g. in order to implement an IP protection) and/or for aesthetic reasons.
As shown in FIG. 8b, typically LEDs L (and optionally regulator 24) are mounted onto a first face of the printed circuit 202, while on the opposite face there may be provided a heatsink 206, typically of a metallic material.
The inventors have observed that the previously discussed lighting systems may cause an apparently inexplicable malfunction or failure.